Angular Distributions Of Protons Research Articles

Model description data of trapped radiation as used to estimate the west-east asymmetry effect in the Brazil magnetic anomaly

Exposure of spacecraft presented as two semi-spherical layers of different inside diameters to radiation-belt protons is simulated. The proton angular distributions are calculated by converting the global trapped-proton flux defined by the model description (Russian State Standard 25645.138-86), making allowance for the proton flux west-east asymmetry. The calculation results have shown that the occurrence of the west-east asymmetry effect at altitudes of < 500 km in the Brazil magnetic anomaly permits the equivalent dose received by a crew to be reduced additionally by a factor of 1.5-2.0 by means of an appropriate reorientation of a spacecraft and the choice of an optimal distribution of the shielding matter masses.

Study of J /Ψ three-body decays involving baryons and a pseudoscalar meson in the diquark model

The J/Ψ decay into a baryon pair and a pseudoscalar meson is computed, for some channels, in lowest order in perturbative QCD, modeling the baryon with a quark-diquark system. We use a set of parameters that has been proposed by some authors in order to fit the proton magnetic form factor GMP, the angular distribution of protons in the processes γγ → pp, γp → γp and the width of η_c → γγ.

Projectile angular distribution in single ionization of helium by proton impact at high and intermediate energies

The CDW-EIS theoretical method is applied to explain recent measurements of helium single ionization by proton and deuteron impact. This theory can cope with the proton angular distribution data for a wide range of projectile energy from 100 keV to 6 MeV . At intermediate energies the CDW-EIS is shown to considerably improve the first Born approximation. The theoretical angular differential cross sections consider the internuclear interaction required for large scattering angles. A seminumerical technique for the introduction of the internuclear interaction is developed.

Proton scattering by 8He and neutron halo effects

Abstract The existing experimental data on 8He+p elastic and inelastic scattering at low and high energies have been analyzed in terms of an eikonal approach with different presentations of nuclear density distributions. Comparison of calculations with experimental data reveals a sensitivity of recoil proton angular distribution at large momentum transfer to the shape of matter distribution. The root-mean-square redius of 8He has been deduced and effects of neutron halo in 8He are discussed.

Proton angular distribution following multiphoton dissociative ionization of H2.

Proton angular distribution following multiphoton dissociative ionization of H2.

Measurements of quasi-elastic pion single charge exchange on 3He at T π = 245 MeV

Differential cross sections from 3He( π ±, π 0) and 3He( π ±, π 0p) measurements are presented. The π 0 energy spectra from 3He( π ±, π 0) and 3He( π +, π 0p) are characteristic of quasi-free reactions. The proton angular distribution from 3He( π +, π 0p) also show evidence of a quasi-free mechanism. Indications of multi-nucleon processes are presented in the 3He( π −, π 0p) data. At least two nucleons must be involved. Comparisons between coincidence and single-arm measurements from this work and previous measurements of charged pion scattering on 3He provide evidence of an enhanced multiple scattering contribution to the charge exchange channel.

Isospin splitting in analog giant resonances excited by single pion charge exchange reactions

Giant isovector analog E1 resonances have been observed by means of the pion single-charge-exchange reactions ( π ±, π 0). The giant T = 1 analog E1 resonances in 12B and 12N, built on the ground state of 12C, were observed in the 12C( π ±, π 0) reactions. The giant T = 3 2 resonances in 13B and 9Li, built on the ground states of 13C and 9Be, were studied with the 13C, 9Be( π −, π 0) reactions, respectively. Analogs of these resonances were found in the 13C, 9Be( π +, π 0) reactions along with lower lying T = 1 2 resonances. These resonances together with the higher T = 3 2 resonances constitute isospin-splitting in the nuclei, 13N and 9B. These isospin assignments were made by comparing results from the ( π ±, π 0) reactions and their measured angular distributions. The assignments were confirmed by determining the decay properties of the resonances with coincident ( π 0p) measurements in the ( π +, π 0p) reactions. The proton angular distributions measured relative to the momentum transfer direction were consistent with a dipole process.

The (e,e′p0) coincidence cross section for 12C at transfer energy of 40 MeV

Abstract The energy spectra and angular distributions of protons from the 12C(e,e′p) coincidence reaction have been measured at azimuthai angles of φp= −45° and −135° out of the scattering plane, at energy transfer of 40 MeV and momentum transfer of 0.35 fm−1 (69 MeV/c). The longitudinal-transverse interference term, as well as the non-interference term of the (e,e'p0) cross section have been obtained, and the transition amplitudes are deduced in the LS coupling basis. The cross sections are compared with an RPA calculation. The photo-reaction cross section derived from the transverse term is in reasonable agreement with previous experimental results.

Angular distribution of ions axially channeled in a very thin crystal: Experimental and theoretical results.

We have studied the angular distributions for 6--30-MeV C[sup [ital q]+] ([ital q]=4--6) and 2--9-MeV H[sup +] ions axially channeled in the [001] direction of a thin silicon crystal (1792 and 1900 A). We report highly structured two-dimensional angular distributions that depend sensitively on the projectile's velocity and incident charge state and the target's thickness and azimuthal orientation. Some structure in the angular contour maps is the result of a rainbow effect in axial channeling (i.e., extrema in the classical deflection function). State-to-state charge-state distributions, which are required to interpret the data accurately, have also been measured. All measured angular distributions have been explained via Monte Carlo trajectory calculations using Moliere's approximation to the Thomas-Fermi screening function and a screening length given by target electrons alone. The calculations indicate that all projectile velocity and charge-state effects and the target-thickness effects observed are the result of the projectile's transverse oscillatory motion in the channel. Using this information, we show that swift heavy-ion and proton angular distributions are simply related using a scaling law that depends only on the projectile's velocity and charge-to-mass ratio and on the crystal thickness.

The reaction 3He( γ, pp) n at low neutron recoil momentum

The reaction 3He( γ, p) n was measured at the ALS-Saclay at kinematics corresponding to mean neutron recoil momenta near 30 and 75 MeV. Differential cross sections were obtained for photon energies between E γ = 200 and 450 MeV at proton emission angles relative to the p− p center of mass of 49° and 75°, and a proton angular distribution was obtained at E γ = 350 MeV. The cross section for photon absorption by a p− p pair is found to be lower by two orders of magnitude compared to that for a p− n pair in 3He. Theoretical multiple scattering calculations reproduce the data rather well, except for significant discrepancies at low E γ and forward proton angles.

Impact parameter dependence of preequilibrium particle emission.

The energy spectra and angular distributions of protons, deuterons, tritons, and alpha particles from 215 MeV [sup 16]O bombardment of Tb, Ta, and Au have been measured in coincidence with both evaporation residues and fission fragments. The evaporation residue and fission fragment triggers together with the angular momentum dependence of the evaporation residue-fission competition have enabled us to extract the impact parameter dependence of the light charged particle preequilibrium multiplicities within the fusionlike impact parameter domain. The light charged particle spectra can be parametrized as originating from a source with approximately 1/2 to 2/3 of the beam velocity and with a slope parameter of [similar to]5--7 MeV. The proton multiplicities increase with decreasing impact parameter, in agreement with a nucleon exchange transport model prediction. The ratio of the complex particle to proton multiplicities decrease with decreasing impact parameter, suggesting dynamical effects in the complex particle production mechanism.

Study of intranuclear collision effects in interactions ofK +/π + mesons with Al and Au nuclei at 250 GeV/c

Multiplicity, inclusive, correlation and collective characteristics of multiparticle production processes inK+ Al,K+ Au, π+ Al and π+ Au interactions at 250 GeV/c are studied with the European Hybrid Spectrometer, providing high statistics and almost 4 π acceptance for final state charged particles. It is shown that the proton energy spectrum practically does not depend on the target atomic weight, but the proton angular distributions reveal a strongA-dependence. In a model independent way, the average number of intranuclear collisions is extracted, and it is shown that their dominant part (60% for Al and 80% for Au) is caused by interactions of the non-leading particles produced in the target fragmentation. The multiplication ratio of the produced particles for the Au nucleus changes fromR≃40 at the smallest rapidities in the target fragmentation region, down toR=0.37±0.06 at the largest rapidities in the beam fragmentation region. It is found that the average total longitudinal momentum of the charged products of the beam fragmentation depends weakly on the number of leading hadron (cluster) intranuclear collisions which are characterized by a low inelasticity coefficient 〈k〉=0.17±0.03.

Axial channelling of low-energy antiprotons

Monte Carlo computer simulation of the passage of antiprotons and protons through a silicon crystal under axial channelling conditions is performed. The energy spectra and angular distribution of channelled protons and antiprotons moving along the (110) direction are calculated and compared. The projectile energy range is from 300 keV to several megaelectronvolts. It is shown that the energy loss corresponding to the maximum of the antiproton spectrum is close to the energy loss of particles moving in a random direction. Moreover, the most probable energy loss of the channelled part of the antiproton beam is slightly less than the random energy loss. The Barkas correction to the energy loss has little effect on the energy spectra of channelled particles and can hardly be studied with this type of experiment. The angular distributions of protons and antiprotons differ considerably. The characteristic features of the angular distribution may serve as evidence of channelling of low-energy antiprotons.

The penetration of protons with energies of 300 to 500 keV through thin silicon crystals

Angular distributions of protons ( E = 440 keV) behind a thin (1.3 to 2 μm) 〈111〉 silicon single crystal have been measured for different angles of incidence. It is shown that for a target thickness of 2 μm and for the angle of incidence φ equal to ψ L the angular distributions are still anisotropic. The energy losses of protons for φ = 1.6 ψ L and for different detection angles have been found. A reduction of energy losses for the direction parallel to the 〈111〉 axis has been revealed, which indicates the presence of a channeling fraction of the beam. For energies of 340, 440 and 550 keV, angular distribution of energy losses were measured for 〈111〉 Si. It is shown that their differences are due to different diffusion rates in the space of transverse energies. Results obtained for the proton beam directed in both channeling and random directions have been compared to existing experimental and theoretical data.

Angular distribution of fast protons from the pre-equilibrium process of the 165Ho( alpha,p) reaction.

The concept of the exciton model for nucleon-induced nuclear reactions has been extended to \ensuremath{\alpha}-induced pre-equilibrium reactions in order to calculate angular distributions and energy spectra of fast ejectile nucleons. The effect of the nucleon motion on the cascade nucleon-nucleon scattering inside the nucleus and the geometrical optical effects at the exit channel are taken into account for the first time in the \ensuremath{\alpha}-induced pre-equilibrium reaction. Angular distributions of protons from the $^{165}\mathrm{Ho}$(\ensuremath{\alpha},p) reaction at ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=109 MeV were calculated. The observed distributions of the fast protons in the pre-equilibrium region were found to be reproduced well by the calculation.

Proton angular distributions and highly differential cross sections for ionization of helium by proton impact.

The eikonal distorted-wave method is applied to single ionization in proton-helium collisions at laboratory energies of 300 keV, 500 keV, 1 MeV, and 3 MeV. The angular distributions of scattered protons agree well with recent experimental results, showing substantial improvement over the plane-wave Born approximation especially at large scattering angles \ensuremath{\Theta}. The momentum distributions of the ejected electrons at fixed values of \ensuremath{\Theta} are calculated. In particular, those of the electrons ejected mainly in binary proton-electron collisions are studied in detail. The momentum distributions of the recoil ${\mathrm{He}}^{+}$ ions at fixed values of \ensuremath{\Theta} are also discussed by comparing with the results of recent coincidence measurements. At such small \ensuremath{\Theta} at which the plane-wave Born and the eikonal distorted-wave approximations give nearly the same cross sections and are expected to be accurate, these approximations lead to average momenta of recoil ions significantly lower than the measured values.

Preequilibrium versus thermalized light-charged particle emissions in the40Ar (1100MeV)+24Mg reaction. Dynamical calculations

In an attempt to separate preequilibrium and thermalised emissions of light particles in low impact parameter heavy-ion collisions, the40Ar+24Mg reaction has been studied at 27.5 MeV/nucleon. Exclusive measurements have permitted us to examine, in some detail, heavy fragments and charged particles (p, d, t,α-particle). The fragments recognized as evaporation residues have been selected and, due to inverse kinematic conditions, the related preequilibrium and statistical emissions of light particles resulting from incomplete fusion reaction appear to be distinguishable to a fair extent. This separation is fully supported by Monte Carlo calculations. Some experimental characteristics of the light particles have been examined and compared to the predictions of dynamical calculations. These calculations, associating a preequilibrium (interpreted as prompt emitted particles) model with a statistical-decay model, follow the evolution of the collision from the point of contact between the projectile and the target to the final evaporation-residue formation on an event by event basis. The predictions of these calculations have been compared to experimental data and satisfactory agreement is achieved for fragment-mass distribution, proton-energy spectra, and proton-angular distribution.

Structure of the Triplet of low-lying states in101Mo

The properties of the triplet of low-lying states in101Mo have been studied through spectroscopy of theγ radiation following thermal neutron capture in100Mo and β− decay of101Nb and through a measurement of the proton angular distributions in the100Mo(d,p) reaction with 14 MeV deuteron energy. The half-lives of the 13.5 keV state and the 57.0 keV 5/2+ state have been measured as 226(7) and 133(7)ns, respectively. These values and the quadrupole/dipole mixing ratios of the 13.5 keV and 43.5 keV transitions yield spin and parity 3/2+ for the 13.5 keV level. The E2 components in the 13.5 (3/2+ →1/2+) and 43.5 keV (5/2+→3/2+) transitions are ≦ 8·10−4 and 54(9)%, respectively. The possibility of an additional state near to the 57.0 keV level is discussed. IBFM/PTQM calculations, taking into consideration the transitional character of the100Mo boson core, account for the electromagnetic-transition and transfer-reaction pattern of the triplet of states.

Spectroscopic information on 13,14C, 15N, 17O, 29–31Si, 33S, 28Cl and 111,113,115,117Cd from the (d,p) reaction

Abstract The accurate and precise (d, p) reaction Q-values and excitation energies corresponding to 98 states of final nuclei 13,14 C, 15 N, 17 O, 29–31 Si, 33 S, 38 C1 and 111,113,115,117 Cd are presented as a result of high resolution experiments performed with 12.3 MeV deuterons. The protons were analysed by multi-angle magnetic spectrograph. The resolving power E ΔE of about 2000 and accurate calibration of spectra allowed to get the energies of most states with higher precision than is presently known. Angular distributions of protons from the reaction 37 Cl(d, p) 38 Cl were analysed using DWBA calculations. Revised values of transferred orbital angular momenta and spectroscopic factors for 25 states of 38 C1 are given. Single-particle strengths for If and 2p orbitals are compared with respective single-particle strengths from the reaction 36 S(d, p) 37 S. Sum rules indicate that substantial parts of 1f and 2p single-particle strengths are exhausted by states observed in present experiment.

Limiting excitation energy in the reaction Si+Si

We have measured energy and angular distributions of protons and α-particles in coincidence with evaporation residues for the reaction Si+Si at beam energies 12.4, 19.7, and 30.0 MeV/N. The reconstructed excitation energies of composite systems decaying into evaporation residues saturate near 3 MeV/N with increasing beam energy. This is consistent with a limiting excitation energy between 4 and 5 MeV/N above which sequential evaporation does not occur.